In a known manner, the annular combustion chamber of the turbomachine is situated in an annular space delimited by an internal casing and an external casing. The internal casing supports the diffuser whose inlet is aligned with the outlet of the centrifugal compressor and whose outlet is situated radially outside the combustion chamber.
The air coming out of the diffuser is intended primarily to enter the combustion chamber and be mixed with fuel and then burnt, and secondarily to travel round the combustion chamber to supply primary and dilution orifices of the chamber and air injection means for ventilating and/or cooling components, particularly of a turbine, situated downstream of the combustion chamber.
The diffuser is connected to an annular end-piece with a substantially L-shaped section forming the internal casing that extends downstream to the aforementioned air injection means. The internal casing delimits, with the internal wall of the chamber, an annular cavity having a relatively large volume and the air that travels round the chamber passing between the latter and the internal casing is not guided and is subjected to turbulence and separations of flow that cause pressure losses and reduce the performance of the turbomachine. This phenomenon is amplified when the chamber is inclined inward from upstream to downstream.
However, it is not possible to envisage modifying the shape of this internal casing in order to attempt to prevent these disadvantages, because this casing is a structural part that supports components and that transmits forces, so that its shape cannot be changed markedly without degrading its structural functions and without greatly increasing its weight. Furthermore, this modification would be costly.